Studies are being performed on the isoenzymic forms of dynein from sea urchin sperm flagella. Dynein 1 constitutes the outer arms on the doublet tubules of the flagellar axoneme, and can be extracted selectively with 0.6 M NaCl at pH 7.0. The 21S form of dynein 1 has a particle weight of approximately 1,250,000 daltons, and contains 2 heavy chains (A alpha and A beta) of approximately 350,000 daltons, 3 intermediate chains, and at least 4 light chains. Dynein 2 can be extracted selectively by dialysis at low ionic strength at pH 6.0, or with 1 M LiCl at the same pH. The solubilized dynein 2 sediments at approximately 11S, but its subunit composition has not yet been determined. We intend to purify dynein 2, and determine its localization in the axoneme. Steady-state and presteady-state kinetics of the two dynein isoenzymes are being studied in order to clarify the steps in the dynein cross-bridge cycle that generates active slidng between the doublet tubules. The absence of dynein arms is frequently the molecular factor underlying the recently recognized congenital defect known as the "immotile-cilia syndrome".